Conventionally, as a mechanical seal device, a static pressure mechanical seal device preventing a fluid sealed inside a machine from leaking toward the outside of the machine is known. For such static pressure mechanical seal device, by supplying higher purge gas on a seal surface compared to the sealed fluid, the purge gas is leaked toward the inside and the outside of the machine, with the result that the seal fluid is prevented from leaking toward the outside of the machine.
However, in a conventional static pressure mechanical seal device, due to a pressure fluctuation inside of the machine, a balance between the pressure inside of the machine and the pressure of the purge gas is broken, with the result that it tended to be difficult to properly maintain a clearance between sliding surfaces. For example, as the pressure inside of the machine is higher than the predetermined pressure, the clearance between the sliding surfaces is opened more than necessary, with the result that the sealed fluid might be leaked toward the outside of the machine. Further, as the pressure inside of the machine is lower than the predetermined pressure, it causes contacts of sliding surfaces, with the result that the sliding surfaces tended to be damaged.
In order to solve the above problems, for example, a mechanical seal device as illustrated in Patent Document 1 is suggested. In the mechanical seal device of Patent Document 1, a back-pressure introduction passage communicating between a region inside of the machine and a back region of a stationary seal ring is formed. However, for the conventional mechanical seal device of Patent Document 1 and the like, a plurality of O-rings needs to be arranged between the stationary seal ring and a seal case and that resulted in a decrease in an axial synchronized movability rate (synchronized movability deteriorates) of the stationary seal ring.
Further, in the conventional mechanical seal device of Patent Document 1 and the like, cloggings occur in the back-pressure introduction passage formed narrow and long, so that there was a problem that the pressure of the sealed fluid could not be applied on the back face of the stationary seal ring. Further, components included in the sealed fluid stick to the operational O-rings, springs and the like arranged in the back region of the stationary seal ring, with the result that the axial synchronized movability of the stationary seal ring deteriorate.
Patent Document 1: WO99-27281